Manufacturing of semiconductor devices requires the formation of electrical connections between conductive regions on a surface of a substrate. Generally, a series of non-conductive dielectric films are formed on the surface of the substrate which overlie electrically connected conductive regions. The conductive regions include electrical devices or electrical interconnection lines. Interconnection lines electrically connect different electrical devices on the substrate and allow for electrical contact to external leads.
FIG. 1 shows a semiconductor device. The semiconductor device includes a substrate 10 and an electrical device 12. The semiconductor device further includes interconnection lines 14, 16, 18, 20. A metal layer 22 electrically connects the electrical device 12 with interconnection line 18. A first dielectric layer 24 and a second dielectric layer 26 provide insulation between the electrical device 12, interconnection lines 14, 16, 18, 20 and the metal layer 22. Layer 24 can include a low-dielectric constant layer having adhesive layers on either side. When applying dielectric layers it is desirable to create a uniform surface, as close to a level, planar surface as possible, so as to facilitate the coverage of subsequent layers.
One of the best methods for deposition of dielectric films is known as chemical vapor deposition. This process forms solid films on substrates by the reaction of vapor phase chemical on the semiconductor surface. Chemical vapor deposition processes are preferred over other methods because they are more economical and because they allow for easy control over the deposition process. Chemical vapor deposition methods provide a high purity of deposited material and tend to have better fill capabilities than other methods of forming films.
FIG. 2 shows a processing chamber 30 used for chemical vapor deposition. A semiconductor wafer 32 is placed onto a heating block 36 within the processing chamber 30. A gas feed 34 releases a composition of reactive gases and inert gases into the processing chamber 30 through nozzles 35 of a powered electrode 37. Upon reaction, these gases move onto the surface of substrates included on the semiconductor wafer 32. An exit pump 39 allows for removal of the gases. Pins 33 are used to separate the wafer 32 from the heating block 36 and to aid in the placement and removal of the wafer 32 within the chamber 30.
Plasma Enhanced Chemical Vapor Deposition (PECVD) methods can be used to deposit layers of silicon-dioxide (SiO.sub.2) film. PEVCD methods for depositing films provide fast deposition rates and good step coverage. PEVCD methods require an rf-induced glow discharge provided by the powered electrode 37 which is connected to an rf-power supply 38. The rf-power supply 38 allows the transfer of energy to the reactive gases.
Silicon-dioxide (SiO.sub.2) films have a dielectric constant of about 4.0. The dielectric constants of the films on a substrate determine the distributed capacitance associated with interconnections lines on the substrate. The distributed capacitance associated with the interconnection lines determines the operable frequency of electrical signals coupled through the interconnection lines. That is, the greater the distributed capacitance associated with the interconnection lines, the lower the operable frequency of the electrical signal coupled through the interconnection lines. The distributed capacitance associated with the interconnection lines can be reduced by reducing the dielectric constant of the deposited films. Reducing the dielectric constant of deposited films increases the operable frequency of electrical signals coupled through the interconnection lines.
It is desirable to have a method of forming dielectric films over a substrate which have lower dielectric constant than presently existing films. Further, the method would provide the benefits of present PEVCD methods.